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Viola key for fruiting and cleistogamous flowering material
See list of 30 species in this subkey-
1a. Plants acaulescent, the leaves and peduncles borne directly from rhizomes or stolons [Figs. 933,936]
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2a. Plants producing stolons, these naked or with tiny leaves, often also with cleistogamous flowers from the nodes
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3a. Stolons leafy; capsules densely pubescent; seeds 3.4–4 mm long; rhizomes mostly 2–4 mm wide
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3b. Stolons naked or with few leaves; capsules glabrous; seeds 1–2.1 mm long; rhizomes 1–2 (–3) mm wide
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4a. Leaf blades 1.5–7 times as long as wide, narrow-cuneate to subcordate at the base
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5a. Leaf blades 3–7 times as long as wide, narrowly tapering at the base, the margins denticulate, each tooth with a distinct red-black to black gland at the apex
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5b. Leaf blades 1.5–2.5 times as long as wide, broader at the base, widely tapering to truncate or subcordate at the base, the margins crenate, the teeth with inconspicuous, pale glands
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4b. Leaf blades up to 1.5 times as long as wide, cordate at the base
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6a. Leaf blades pubescent on one or both surfaces, sometimes sparsely so; capsules spotted or suffused with purple to purple-brown [Fig. 929], the cleistogamous ones borne on prostrate to low-arching peduncles; seeds 1.6–2.1 mm long
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6b. Leaf blades glabrous on both surfaces; capsules green (often with minute orange dots in V. pallens) [Fig. 934], the cleistogamous ones borne on ascending to arching peduncles; seeds 1–1.7 mm long
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7a. Seeds 1–1.4 mm long, brown to nearly black
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7b. Seeds 1.5–1.7 mm long, light gray to light brown
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2b. Plants not producing stolons
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8a. Rhizomes horizontal to ascending, elongate, slender, mostly 1–3 mm thick
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9a. Leaf blades cordate-ovate to cordate-suborbicular, acute to obtuse at the apex; basal sinus of leaf blade either narrow or with converging to overlapping lobes; stipules connate to the petiole for a short distance; seeds 1.5–1.9 mm long
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9b. Leaf blades cordate-orbicular to reniform, rounded to obtuse at the apex; basal sinus of leaf blade wide open; stipules distinct from the petiole; seeds 1.9–2.4 mm long
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8b. Rhizomes usually ascending, short, stout, mostly 4–6 mm thick
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10a. Leaf blades with conspicuous lobes (though the first leaves to appear in V. palmata are unlobed)
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11a. Leaf blades oblong-lanceolate to ovate-triangular, 1.5–3 times as long as wide, coarsely serrate to divided into short lobes at the base [Fig. 936]; lobes, if present, less than 50% of the total length of the leaf blade (in part)
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11b. Leaf blades ± ovate in outline, less than 1.5 times as long as wide, with evident lobes (except for the first leaves to emerge which may be unlobed to weakly lobed); lobes often greater than 50% of the total length of the leaf blade
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12a. Capsules green [Fig. 934]; sepals lanceolate, narrow-acute to acuminate at the apex, eciliate or ciliate
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13a. Foliage pubescent; rhizome fleshy, barrel-like; cleistogamous flowers not produced; sepals usually ciliate
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13b. Foliage glabrous; rhizome ± firm, not barrel-like; cleistogamous flowers produced—these recognized by the coiled style; sepals eciliate [Fig. 930]
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12b. Capsules spotted or suffused with purple to purple-brown on a green background [Fig. 929]; sepals ovate, rounded to obtuse at the apex, usually at least sparsely ciliate [Fig. 937]
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10b. Leaf blades all unlobed
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15a. Leaf blades 1.5–3 times as long as wide, truncate to subcordate at the base, usually more coarsely serrate or even somewhat lobed at the base of the blade (especially in later season leaves; not so in V. japonica)
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16a. Stipules distinct; roots white-brown to yellow-brown; leaf blade not, or scarcely, decurrent on the petiole (in part)
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16b. Stipules connate to the petiole; roots dark brown; leaf blade decurrent on petiole
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15b. Leaf blades commonly less than 1.75 times as long as wide, definitely cordate at the base, the teeth at the base of the blade no more obvious than those along the middle of the blade margin (except in V. pectinata)
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17a. Leaves on spreading petioles, nearly flat to the ground; stipules entire; cleistogamous flowers borne on a horizontal, late-appearing stem, usually 2 or more, the stem appearing raceme-like
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17b. Leaves mostly on ascending petioles, held above the ground; stipules ciliate-toothed on the margin; cleistogamous flowers borne singly at the summit of a peduncle
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18a. Leaf blades with prominent, coarse (i.e., almost lobe-like) teeth near the basal margins that gradually become shorter and narrower toward the apex
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18b. Leaf blades with rather uniform teeth along the margin
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19a. Leaf blades longer than wide, acute to short-acuminate at the apex; sepals eciliate [Figs. 930,934]
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20a. Sepal auricles 2–5.3 mm long on cleistogamous fruits; cleistogamous flowers borne on ascending peduncles; capsules green, 10–15 mm long; seeds dark brown to black-red or olive-black
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20b. Sepal auricles 0.5–1.6 mm long; cleistogamous flowers borne on peduncles that are at first prostrate, later ascending from a declined base; capsules spotted or suffused with purple, 6–10 mm long; seeds light yellow-brown to brown (infrequently to dark brown in V. sororia)
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21a. Sepals narrow-ovate, rounded to obtuse at apex; peduncles often pubescent; capsules glabrous; seeds brown, sometimes with darker brown markings (rarely yellow-brown)
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19b. Leaf blades as wide as or wider than long, mostly rounded to obtuse at the apex; sepals usually ciliate (eciliate in V. nephrophylla) [Fig. 937]
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22a. Leaf blades glabrous; peduncles of cleistogamous capsules ascending, not declined at base; capsules green
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22b. Leaf blades usually with some hairs on one or both surfaces; peduncles of cleistogamous capsules at first prostrate (or even subterranean), later ascending from a declined base; capsules spotted or suffused with purple
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23a. Pubescence of leaves consisting of silver hairs concentrated on the adaxial surface, the abaxial surface and petioles glabrous or nearly so; leaves usually rounded at apex, often suffused with purple
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23b. Pubescence of leaves variable, but not concentrated on adaxial surface and often found on the petioles; leaves rounded, to more commonly, obtusely to acutely pointed at apex, without purple coloration
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1b. Plants with leafy aerial stems, the peduncles arising from the axils of leaves [Fig. 935]
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24a. Plants annual from an erect taproot; stipules foliaceous and prominently lobed in a pinnatifid fashion
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25a. Lower leaf blades usually truncate to subcordate at the base; capsules (6–) 6.5–9.5 mm long
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25b. Lower leaf blades usually broad-cuneate to truncate at the base; capsules 4–6.5 mm long
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24b. Plants perennial from rhizomes; stipules scarious to herbaceous or subfoliaceous, entire to lacerate-toothed along the margin [Fig. 935]
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26a. Stipules scarious to herbaceous, entire to dentate or undulate; capsules 5–12 mm long; stems often produced singly at the summit of the rhizome
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27a. Stipules scarious or subscarious, pale, entire; capsules 5–10 mm long; seeds 1.5–2.2 ×1.2–1.5 mm
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27b. Stipules herbaceous, green, mostly dentate or undulate; capsules 10–12 mm long; seeds 2.5–3.2 ×1.5–1.8 mm
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26b. Stipules herbaceous or subfoliaceous, fimbriate to lacerate-toothed (entire in high-elevation plants of V. labradorica); capsules 4–6 mm long; stems often clustered together at the summit of the rhizome
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28a. Sepals ciliate; leaf blade margins with closely set, crenulate teeth
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28b. Sepals eciliate [Figs. 930,934]; leaf blades variously subentire to remotely or regularly crenulate
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29a. Upper stem leaf blades narrow-ovate, tending to be acuminate at the apex; seeds mostly 1.1–1.4 mm thick
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29b. Upper stem leaf blades triangular-lanceolate to ovate or orbicular, rounded to acute at the apex; seeds mostly 0.8–1.1 mm thick
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30a. Leaves commonly sparsely to densely pubescent, the hairs never restricted to the adaxial ( i.e., upper) surface only, the blades dark blue-green to dark gray-green in life, subcoriaceous, often with a revolute margin, the upper blades ovate to triangular-lanceolate and mostly truncate at the base; petioles distinctly winged; seeds dark brown to olive-black, mostly 0.8–1.0 mm thick
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30b. Leaves commonly glabrous, when pubescent the hairs restricted to the adaxial surface, the blades light green in life, thin, not or barely revolute, the upper blades usually ovate to orbicular, with a cordate base; petioles not distinctly winged; seeds light brown to brown (dark brown), mostly 1–1.1 mm thick
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Each photo represents one species in this subkey.